1. Field of the Invention
The invention relates generally to a differential amplifier and, more particularly, is directed to an improved differential amplifier with a current mirror type constant current circuit.
2. Description of the Prior Art
It has been known to provide a differential amplifier with a current mirror circuit as its load and which is used in a stereo demodulation circuit or the like, for example, as disclosed in my U.S. patent application Ser. No. 731,018, filed Oct. 8, 1976, for "MPX Stereo Signal Demodulator," and which has a common assignee herewith. In general, such known differential amplifier reduces its load current and common impedance current simultaneously to stop the amplification operation of the differential amplifier (so-called muting operation) when a feeble input signal is applied thereto. In such case, if there is a difference or so-called off-set current between the load current and the common impedance current, the output DC voltage of the differential amplifier fluctuates and a noise may be produced. Therefore, it is necessary to reduce the mentioned off-set current as much as is possible.